Study On The Fabrication,Microstructure And Properties Of 6092Al Matrix Composites Reinforced By Particles With High Volume Fraction

Particle reinforced Al matrix composites have the advantages of low density,high specific strength,excellent wear resistance,controllable thermal expansion coefficient and so on,and are widely used in aerospace,rail transportation,weapons and equipment and other fields.However,particle reinforced Al matrix composites prepared by traditional process have some problems such as uneven particle dispersion,serious interfacial reaction and low mechanical properties.In order to solve the above problems,the preparation process,microstructure and mechanical properties of 6092Al matrix composites reinforced with high volume fraction silicon carbide particles（Si C_p）and/or lithium nepheline particles（Euc）were studied based on spray forming and die forging process.Optical microscopy（OM）,X-ray diffraction（XRD）,scanning electron microscopy（SEM）and transmission electron microscopy（TEM）were used to observe and analyze the particle distribution,phase composition,interface structure and dislocation distribution of the composites.The mechanical and thermophysical properties of the composites were tested by electronic universal testing machine,thermal dilatometer and thermal conductivity meter.This thesis mainly carries out the following research work:（1）Die forging process and heat treatment process parameters are studied.The die forging densification process of spray forming high volume fraction particle reinforced Al matrix composites was explored.The optimum die forging parameters were obtained as follows:die forging temperature 510℃,die forging pressure 8 MPa and holding time 20 min.The particles in the composite prepared by this process were evenly distributed without agglomeration,the density was up to 99.81%,and no obvious holes were found at the interface.The optimal heat treatment parameters were obtained as follows:solution at 520℃for 1.5 h,water cooling;artificial aging at 170℃for 3 h,air cooling.（2）The microstructure of the composites was studied.The results show that the interface between Si C_p/Al and Euc/Al in（45 vol.%Si C_p+5vol.%Euc）/6092Al matrix composites is clean and smooth,and the overall bonding is good,and no interface reaction is observed.Si C_p/Al interface is semi-coherent interface formed by compact atom matching,while Euc/Al interface is non-coherent interface.There are high density dislocations and Mg₂Si strengthening phases near Si C_p/Al and Euc/Al interfaces.（3）The mechanical properties of the three composites at room temperature were studied.The results show that the bending strength of45 vol.%Si C_p/6092Al,5 vol.%Euc/6092Al and（45 vol.%Si C_p+5 vol.%Euc）/6092Al matrix composites are 494 MPa,302 MPa and 485 MPa,respectively.The bending modulus of the three composites are 113 GPa,46 GPa and 96 GPa,respectively.The tensile strength of the three composites is 357 MPa,273 MPa and 315 MPa,respectively.At the same time,the effect of heat treatment process on the mechanical properties of the three composites at room temperature was studied.After solution at520℃for 1.5 h and artificial aging at 170℃for 3 h,the mechanical properties of the three kinds of composites were improved to a certain extent compared with the forging state.The tensile fracture of 6092Al alloy and three kinds of composites was observed.It was found that the fracture mode of 6092 Al alloy was ductile fracture,and the fracture mode of three kinds of composites was brittle and ductile mixed fracture.（4）The thermal physical properties of three kinds of composites were studied.The effect of heat treatment process on thermal expansion coefficient of three kinds of composites was studied.After 520℃solution for 1.5 h and 170℃artificial aging for 3 h,the thermal expansion coefficient of the three kinds of composites changed little compared with the forging state.The thermal expansion coefficient of the（45 vol.%Si C_p+5vol.%Euc）/6092Al matrix composites is the lowest(14.68×10^-6·k^-1)and the highest(190 W·m^-1·K^-1)in the aged state.The addition of Euc particles can significantly reduce the thermal expansion coefficient of the composite.